1. Field of the Invention
The present invention relates to the fields of molecular biology, and reproductive technology. In particular, the invention relates to a cation channel protein expressed specifically in sperm cells, to nucleic acids encoding the protein, cells engineered to express the protein, assays for compounds affecting the activity of the protein, and to the use of such compounds in the treatment or causation of infertility, or as a means of contraception or animal control.
2. Description of the Related Art
Sperm and ova reciprocally interact in mammalian fertilization (Wassarman, et al. (2001), Nature Cell Biology 3, E59-E64; Yanagimachi (1994), in The Physiology of Reproduction, eds. Knobil & Neill (Raven Press, New York), pp. 189-315). To reach the site of fertilization, sperm must travel relatively long distances and become primed for fertilization of the ova through capacitation and other processes. Once they arrive at the surface of an ovum, sperm interact with ovum extracellular matrix glycoproteins including the zona pellucida proteins. Sperm release acidic material during the acrosome reaction, a signaling event that presumably involves the opening of Ca2+ channels and the influx of Ca2+ into the sperm heads (O'Toole, et al. (2000), Mol Biol Cell 11, 1571-84). The TRPC2 protein, a putative Ca2+-permeant channel, has recently been implicated in the acrosome reaction (Jungnickel, et al. (2001), Nat Cell Biol 3, 499-502). Penetration of sperm through the thick outer layer of the ovum is achieved through chemical lysis of the ovum coat and/or the mechanical motion of sperm (Bedford (1998), Biol Reprod 59, 1275-87). Following infiltration of the ovum ZP coat, the sperm membrane fuses with that of ovum. Fusion is followed by activation of the fertilization process, beginning with Ca2+ oscillations in the ovum (Wassarman, et al. (2001), Nature Cell Biology 3, E59-E64; Yanagimachi (1994), in The Physiology of Reproduction, eds. Knobil & Neill (Raven Press, New York), pp. 189-315).
Ca2+ and cyclic nucleotides control sperm motility (Tash (1990) in Controls of Sperm Motility: biological and clinical aspects, ed. Gagnon (CRC Press, Boca Raton), pp. 229-240; Darszon, et al. (1999), Physiol Rev 79, 481-510; Hyne & Garbers (1979), Proc Natl Acad Sci USA 76, 5699-703) and several voltage-dependent Ca2+ channel (CaV) mRNAs and cyclic nucleotide-gated (CNG) channel proteins have been detected in sperm cell precursors (Darszon, et al. (1999), Physiol Rev 79, 481-510; Serrano, et al. (1999), FEBS Lett 462, 171-6; Weyand, et al. (1994) Nature 368, 859-63; Wiesner, et al. (1998), J Cell Biol 142, 473-84). Furthermore, low voltage activated, dihydropyridine-sensitive “T-type” channels (Santi, et al. (1996), Am J Physiol 271, C1583-93; Arnoult, et al. (1996), Proc Natl Acad Sci US A 93, 13004-9) and pharmacologically defined N- and R-type currents have been measured in spermatogenic cells (Wennemuth, et al. (2000), J Biol Chem 275, 21210-7). But the role of these channels in spermatogenesis or mature sperm function is not known.